In digitally based image capturing devices an image or “photograph” of an object is stored in a digital data format in the memory within, or coupled to, the image capturing device. A nonlimiting example of a digital image capturing device is the digital camera that captures still images and/or video images. Captured images are stored in a memory that resides within or is coupled to the digital camera.
Watermarking and other tampering detection techniques are known in the art for protecting the integrity of individual digital images. Tamper detection techniques allow confirmation that the digital image has not been altered or otherwise tampered with.
However, digital images can be altered or otherwise tampered with when the encryption schemes are known by or are broken by unauthorized individuals skilled in the art of encryption technologies.
Many image encryption and decryption technologies are complex. Once implemented, some encryption techniques require a substantial amount of computational capacity and time from the processing device that encrypts and/or decrypts the protected image. Furthermore, when a public/private key system is employed, separate data files must be separately managed in a secure manner to prevent an unauthorized individual from having access to the keys. Other encryption systems may also employ separate files that must be securely communicated to the intended recipient of the decrypted image.
Encryption techniques, such as watermarking, alter information in selected pixels such that the altered pixels contain encryption information. The encryption information is detected electronically during decryption and used for verifying that the image has not been tampered with, forged or otherwise altered. However, the amount of information that can be stored by altering a pixel is limited. If the pixel data is altered too greatly, the altered pixel may be detectable by a person viewing the image. Altering pixel data to a point that is discernable to a person viewing the image is particularly undesirable when important portions of the image are encrypted to provide security. Thus, the degree of allowable pixel alteration is limited to being below the visibility threshold of the person viewing the image if the image is to remain visually pleasing to the viewer after encryption.
Furthermore, once a pixel is altered, such as when a watermark is added, that pixel is communicated to the intended recipient in its altered form. Accordingly, if the intended recipient desires to further process the image, such as by magnification, the watermark may become visible or otherwise hinder further processing of the image. In some encryption systems, restoring the altered pixel to its original, unaltered state is impossible or very difficult to accomplish.